U.S. Pat. No. 3,982,622 granted on Sept. 28, 1976, to Joseph A. Bellino, et al. discloses an actuating mechanism for wire matrix printers. In the Bellino et al. patent a permanent magnet applies a magnetomotive force to a pair of pole structures for normally attracting an armature to the pole structure so as to apply bias to a torsion spring. An adjusting flag at the opposite ends of the torsion spring is mechanically located by an adjusting screw so as to control the amount of spring bias applied to the armature by the torsion spring.
In order to operate the print magnet, a coil is placed loosely around the armature. A pulse of current passing through the coil neutralizes the permanent magnet magnetomotive force in the armature, thus permitting the armature to respond to its spring bias and move away from the permanent magnetic pole structure. An extension on the armature engages the print wire and drives the print wire to impact the ribbon and paper of the printing device in order to print a dot. Simultaneous control of several of these magnets in a timed sequence successfully produces alphanumeric indicia on the paper.